CONFERENCE
Teorētiskās Fizikas Katedras seminārs
Semināra tēma: Synthetic magnetic swimmers: from single individuals to collective effects
(Sintētiski magnētiski peldētāji: no individuāliem peldētājiem līdz kolektīviem efektiem – seminārs angļu valodā) Lektors: Dr. Damien Faivre, Department of Biomaterials, Max Planck Institute of Colloids and Interfaces, Science Park Golm, 14424 Potsdam, Germany Īss pētījuma apraksts: Populations of motile organisms typically display dynamic assembling patterns and collective motions, universal behaviors that are not fully matched by active synthetic matter yet. Actuated colloidal particles have recently emerged as a model to understand the collective motion of living organisms. In such model systems the populations are, however, typically made up of identical particles, in contrary to biological swarms that consist of non-identical individuals. One type of actuated colloids is magnetic micropropellers, for which the motion of individual micropropellers has been investigated extensively, but not their collective motion. By using magnetic micropropellers, we show that not only identical helical propellers but also propellers of varying dimensions and morphologies exhibit dynamic assembly patterns. The propellers reversibly assemble into rotating, circular clusters when moving towards an interface. The cluster formation is thus a generic phenomenon that is not affected by “details” as variability within a group. In addition, we show that the assemblies of random propellers can also exhibit translational motion, with larger assemblies moving faster. This finding is even more striking considering that the assemblies move with speeds surpassing the speed of the individual units they are composed of. Laiks un vieta: Seminārs notiks pirmdien, 2016. gada 17. oktobrī pulksten 16:30, Latvijas Universitātes Fizikas un matemātikas fakultātes laboratoriju korpusa (Zeļļu iela 23) otrajā stāvā, F-213 telpā. Magnētisku Mīkstu Materiālu Laboratorijas seminārs Semināra tēma: Magnetotactic bacteria: taking magnets to swim
(Magnetotaktiskās baktērijas: peldošie magnēti – seminārs angļu valodā) Lektors: Klaas Bente, Department of Biomaterials, Max Planck Institute of Colloids and Interfaces, Science Park Golm, 14424 Potsdam, Germany Īss pētījuma apraksts: Bacteria live at low Reynolds numbers. Special about this environment is that the bacteria have to sample their aquatic environment while overcoming the diffusion of relevant chemicals in order to navigate within gradients of external chemical stimuli. This means that they have to swim a minimum distance, which is the ratio of the diffusion coefficient of a relevant chemical and their swimming speed. Since the bacteria themselves also undergo rotational diffusion during this swim, there is also a maximum distance they can swim in one stable direction, which is the ratio of their swimming speed and their own rotational diffusion coefficient. This results in an interval of biologically useful swim length. The regulation of the lengths of randomly oriented swimming episodes within this interval is the fundamental navigation strategy for most motile bacteria. To overcome the inefficiency of a 3D search strategy magnetotactic bacteria feature chains of intracellular ferromagnetic nanoparticles. It is believed that these chains allow navigation along the geomagnetic field. Due to a continuous realignment with the earth magnetic field, the upper limit of swimming distances can be neglected and a navigation strategy close to a direct search towards growth-favoring zones can be achieved. For the studies of these systems we developed a multi-modal microscopy platform which permits the simultaneous mapping of the chemical environment and the response of the organisms, and the ability to generate a controlled physiological magnetic field. Using fluorescence and high-speed imaging, 2D and 3D tracking and diffusion and aerotactic models, we characterized the magneto-aerotaxis of the bacterium Magnetospirillum gryphiswaldense. Laiks un vieta: Seminārs notiks otrdien, 2016. gada 18. oktobrī pulksten 16:30, Latvijas Universitātes Fizikas un matemātikas fakultātes laboratoriju korpusa (Zeļļu iela 23) otrajā stāvā, F-213 telpā.
(Sintētiski magnētiski peldētāji: no individuāliem peldētājiem līdz kolektīviem efektiem – seminārs angļu valodā) Lektors: Dr. Damien Faivre, Department of Biomaterials, Max Planck Institute of Colloids and Interfaces, Science Park Golm, 14424 Potsdam, Germany Īss pētījuma apraksts: Populations of motile organisms typically display dynamic assembling patterns and collective motions, universal behaviors that are not fully matched by active synthetic matter yet. Actuated colloidal particles have recently emerged as a model to understand the collective motion of living organisms. In such model systems the populations are, however, typically made up of identical particles, in contrary to biological swarms that consist of non-identical individuals. One type of actuated colloids is magnetic micropropellers, for which the motion of individual micropropellers has been investigated extensively, but not their collective motion. By using magnetic micropropellers, we show that not only identical helical propellers but also propellers of varying dimensions and morphologies exhibit dynamic assembly patterns. The propellers reversibly assemble into rotating, circular clusters when moving towards an interface. The cluster formation is thus a generic phenomenon that is not affected by “details” as variability within a group. In addition, we show that the assemblies of random propellers can also exhibit translational motion, with larger assemblies moving faster. This finding is even more striking considering that the assemblies move with speeds surpassing the speed of the individual units they are composed of. Laiks un vieta: Seminārs notiks pirmdien, 2016. gada 17. oktobrī pulksten 16:30, Latvijas Universitātes Fizikas un matemātikas fakultātes laboratoriju korpusa (Zeļļu iela 23) otrajā stāvā, F-213 telpā. Magnētisku Mīkstu Materiālu Laboratorijas seminārs Semināra tēma: Magnetotactic bacteria: taking magnets to swim
(Magnetotaktiskās baktērijas: peldošie magnēti – seminārs angļu valodā) Lektors: Klaas Bente, Department of Biomaterials, Max Planck Institute of Colloids and Interfaces, Science Park Golm, 14424 Potsdam, Germany Īss pētījuma apraksts: Bacteria live at low Reynolds numbers. Special about this environment is that the bacteria have to sample their aquatic environment while overcoming the diffusion of relevant chemicals in order to navigate within gradients of external chemical stimuli. This means that they have to swim a minimum distance, which is the ratio of the diffusion coefficient of a relevant chemical and their swimming speed. Since the bacteria themselves also undergo rotational diffusion during this swim, there is also a maximum distance they can swim in one stable direction, which is the ratio of their swimming speed and their own rotational diffusion coefficient. This results in an interval of biologically useful swim length. The regulation of the lengths of randomly oriented swimming episodes within this interval is the fundamental navigation strategy for most motile bacteria. To overcome the inefficiency of a 3D search strategy magnetotactic bacteria feature chains of intracellular ferromagnetic nanoparticles. It is believed that these chains allow navigation along the geomagnetic field. Due to a continuous realignment with the earth magnetic field, the upper limit of swimming distances can be neglected and a navigation strategy close to a direct search towards growth-favoring zones can be achieved. For the studies of these systems we developed a multi-modal microscopy platform which permits the simultaneous mapping of the chemical environment and the response of the organisms, and the ability to generate a controlled physiological magnetic field. Using fluorescence and high-speed imaging, 2D and 3D tracking and diffusion and aerotactic models, we characterized the magneto-aerotaxis of the bacterium Magnetospirillum gryphiswaldense. Laiks un vieta: Seminārs notiks otrdien, 2016. gada 18. oktobrī pulksten 16:30, Latvijas Universitātes Fizikas un matemātikas fakultātes laboratoriju korpusa (Zeļļu iela 23) otrajā stāvā, F-213 telpā.
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